In many applications it is desirable to capture a micro-organism from a suspension thereof as a first step allowing one subsequently to conduct further work on the micro-organism, e.g. to concentrate a microorganism into a small volume free of impurities and contaminants, for diagnostic purposes for example. The microorganisms may initially be present in a large volume sample material, such as sputum, blood, dispersed food or potable water. Concentration into a small volume that is free of sample contaminants optimises sensitivity and removes inhibitors in diagnostic procedures, such as microscopy, immunoassay or nucleic acid amplifications processes such as PCR. Existing methods to achieve microorganism concentration include the use of paramagnetic beads coated with a microorganism-specific antibody; the beads can be used to specifically capture microorganisms from a sample allowing their subsequent detection by various methods (U.S. Pat. No. 7,166,425).
In some applications, however, the capture conditions may not be suitable for an antibody-based system: for example, in the capture of mycobacteria from sputum that has been thinned with sodium hydroxide and which remains at a high pH which would inactivate antibodies. In these and other circumstances of harsh conditions antibody capture cannot be used. In addition, in other applications it may be desirable to capture any microorganism that may be present in the sample. For example, in sepsis it is important to capture any bacterial or fungal cells that might be present in the blood so that a diagnosis can be made. Similarly, in testing blood products, such as in platelet screening, it is important to know if the blood products (in this case platelets) are contaminated with any microorganism at all. Under such circumstances it would be hard to do this with an antibody-based approach as antibodies tend to be organism or species-specific.
Methods that are not based on antibodies have been described. JP2001112497 describes removing Mycobacteria from an alkali decontaminated liquid by precipitating calcium phosphate therein, the precipitate presumably carrying down the bacteria as it forms. WO 2009/086343 describes the use of a carbohydrate-coated surface together with a biotin binding protein and an amphiphilic glycoside of a steroid or triterpene to bind microorganisms. WO28072242A2 describes a polymeric matrix derivatised with amino acids as a binding surface and WO29046191A2 describes the use of diatomaceous earth particles coated with various metallic or inorganic surfaces to achieve the same result. These methods are more generic than antibody-based approaches but are not truly generic in that some bacterial species are captured better than others and some species or strains of bacteria may not be captured at all. In addition, these methods have not been shown to capture fungi.
These issues are a consequence of relying on the surface property of the binding matrix, which is necessarily limited in nature, to bind bacteria that may have a diverse outer cell wall structure. In this invention, we describe a novel approach that is less dependent in the nature of the surface matrix and has been shown to work with gram positive and gram negative bacteria and fungi in addition to Mycobacteria which tend to have a uniquely hydrophobic cell wall.